A preliminary study of the inheritance of rust resistance in oats

Pedigree lines of two oat varieties, Burt and Sixty-Day, together with a larg number of F2 generation hybrids between these varieties, were studied in relation to their rust resistance. Most of the inoculations were made on seedlings, but enough were made on plants at time of heading to show that the results were similar. The rusts used were the crown rust of oats, Puccinia lolii avenaeMcAlpine, and the stem rust of oats, Puccinia graminis avenae Erikss, and Henn. Burt and Sixty-Day and all the hybrids of these two varieties so far tested were found to be entirely susceptible to stem rust. All plants to Sixty-Day also were uniformly susceptible to crown rust. Of 223 inoculated plants of Burt, 48 were classified as resistant, 152 as intermediate, and 23 as susceptible. Each of the five hybrid families contained, in the F2 generation, some plants showing a high degree of resistance to crown rust and others which were as susceptible as plants of the Sixty-Day parent. In other words, there was definite segregation. There was, however a rather large number of plants which were classified as intermediate and which showed varying degrees of resistance. The numerical results of inoculations made in the F2 hybrids were as follows: seedlings classified as resistant no. 81 (17.3%); seedlings classified as intermediate no. 61 (13.0%); seedlings classified as susceptible no. 326 (69.7%); total no. 468 (100.0%). The fact that there were so many more susceptible than resistant plants indicates that susuceptibility to crown rust in this cross is partially dominant, while resistance is recessive. These contrasted characters are not thought to be due to environmental conditions or to differences in the metabolism of the host plants, but to definite genetic factors. Nonhereditary factors may of course influence or modify their expression. Rust resistance and susceptibility hardly can be considered as simple characters or as being determined by a single factor difference. The F2 generation results, particularly the rather complete series of forms showing varying degrees of resistance and necessarily classified as intermediates, favor the view the several factors are involved, i.e., the multiple factor hypothesis. No attempt has been made to construct a definite factorial hypothesis to explain the results obtained. This preliminary work has proved the possibility of transferring the character of resistance to crown rust from the Burt variety to plants of the F2 generation of a Burt X Sixty-Day cross. This suggests further use of the method of hybridization in the effort to produce rust-resistant varieties of oats for culture in the several oat districts of the United States.